A known sheet separating device includes a support member, a pair of guides, a separation roller, a separation member, and an urging member. The support member supports sheets to be conveyed in a conveying direction. The guides are disposed at the support member while facing each other, and movable relative to each other in a width direction orthogonal to the conveying direction so as to align the sheets with respect to the center of the support member in the width direction. The separation member is urged by the urging member toward the separation roller and separates a sheet from the remaining sheets supported by the support member. The separation roller conveys the separated sheet in the conveying direction.
In the sheet separating device, the separation member is pressed against the separation roller by the urging member, whereby a braking force is generated between the separation roller and the separation member. When two or more sheets are about to be conveyed by the separation roller, a single sheet that is in contact with the separation roller is separated from the other sheets by the braking force acting on the other sheets.